How to add consecutive numbers in a String

Question

I have a String 9899100101103104105 i want to add consecutive numbers i.e 98+99+100...So i am able to cut the numbers from the String and add upto 100.But after that i am sure how to write the logic.I am using String subString() method and i have seen that (0,2),(2,4),(4,7),(7,10),(10,13),(13,16) should be the substring start and end digits.After (4,7) i am not able to proceeed, here is my logic

public class MissingNumberInString {

public static void main(String[] args) {

    String numbr = "9899100101103104105";
    firstTwo(numbr);
 }

public static void firstTwo(String str) {

    int sum =0;
    int  num = 0;
    for(int i=0;i<str.length()-1;i=i+2){

        if(sum <=99){
        sum += Integer.parseInt(str.substring(i, i+2));
        }else{

        sum += Integer.parseInt(str.substring(i, i+3)); 
        }
        System.out.println(sum);
    }

   }
   }

in else part after (4,7) i am not able to proceed ,please help

Might I ask why you are doing this? Is this an assignment and you have to do it? Because otherwise I see no reason why you would concatenate numbers to a string and then try to split/parse those numbers back to Integers again. — user6073886
– user6073886, Commented Oct 18, 2017 at 10:19
is it feasible to change the input (i.e. putting separator chars into the string or using an array of numbers)? — Rhayene
– Rhayene, Commented Oct 18, 2017 at 10:19
You need to increment i based on the sum < = 99 too, you can't increment by 2 after 99... — AxelH
– AxelH, Commented Oct 18, 2017 at 10:21
And who defines that string? Why is it 98 99 103 104 and not 9 89 910 3104? You have a lot of implicit assumptions backed into your questions. You should first step back and really clarify such subtle details. Not only for us, but also for yourself. — GhostCat
– GhostCat, Commented Oct 18, 2017 at 10:25

AxelH · Accepted Answer · 2017-10-18 10:24:13Z

1

Your incrementation failed based on the last value. So keeping your logic :

for(int i=0;i<str.length()-1;i=i+2){
    if(sum <=99){
    sum += Integer.parseInt(str.substring(i, i+2));
    }else{

    sum += Integer.parseInt(str.substring(i, i+3)); 
    }
    System.out.println(sum);
}

You should incremente by 3 when the sum > 99. Do that in the condition block

for(int i=0;i<str.length()-1; /* removed incrementation */){
    if(sum <=99){
        sum += Integer.parseInt(str.substring(i, i+2));
        i=i+2;
    }else{
        sum += Integer.parseInt(str.substring(i, i+3)); 
        i=i+3;
    }
    System.out.println(sum);
}

But honestly, your logic won't be easy to maintain. How do you know that the first value is not 9 and then you should only substring by 1 character first ?

answered Oct 18, 2017 at 10:24

AxelH

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1 Comment

Mandrek Over a year ago

@AxeIH thanks for the fast response your solution worked for me

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